Methyl bromide (MB) was dissolved in peanut oil and given by gavage at 50 mg/kg body weight to Wistar rats five times per week for 13 to 25 weeks. At 25 weeks nearly 100% of the rats receiving MB had hyperplastic lesions of the forestomach which were more severe than at 13 weeks. In the stop treatment group receiving MB for 13 weeks, there was regression of the stomach lesion.